CN110997560A - Method for etching phosphate source with acid - Google Patents

Method for etching phosphate source with acid Download PDF

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CN110997560A
CN110997560A CN201880051613.4A CN201880051613A CN110997560A CN 110997560 A CN110997560 A CN 110997560A CN 201880051613 A CN201880051613 A CN 201880051613A CN 110997560 A CN110997560 A CN 110997560A
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phosphate
etching
liquid phase
calcium
content
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CN110997560B (en
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亚历山大·瓦弗莱勒
利维奥·莱德勒
莱昂·尼南
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Prayon Technologies
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/18—Phosphoric acid
    • C01B25/22—Preparation by reacting phosphate-containing material with an acid, e.g. wet process
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/01—Treating phosphate ores or other raw phosphate materials to obtain phosphorus or phosphorus compounds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/18—Phosphoric acid
    • C01B25/22—Preparation by reacting phosphate-containing material with an acid, e.g. wet process
    • C01B25/222—Preparation by reacting phosphate-containing material with an acid, e.g. wet process with sulfuric acid, a mixture of acids mainly consisting of sulfuric acid or a mixture of compounds forming it in situ, e.g. a mixture of sulfur dioxide, water and oxygen
    • C01B25/223—Preparation by reacting phosphate-containing material with an acid, e.g. wet process with sulfuric acid, a mixture of acids mainly consisting of sulfuric acid or a mixture of compounds forming it in situ, e.g. a mixture of sulfur dioxide, water and oxygen only one form of calcium sulfate being formed
    • C01B25/225—Dihydrate process
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/18—Phosphoric acid
    • C01B25/22—Preparation by reacting phosphate-containing material with an acid, e.g. wet process
    • C01B25/222—Preparation by reacting phosphate-containing material with an acid, e.g. wet process with sulfuric acid, a mixture of acids mainly consisting of sulfuric acid or a mixture of compounds forming it in situ, e.g. a mixture of sulfur dioxide, water and oxygen
    • C01B25/223—Preparation by reacting phosphate-containing material with an acid, e.g. wet process with sulfuric acid, a mixture of acids mainly consisting of sulfuric acid or a mixture of compounds forming it in situ, e.g. a mixture of sulfur dioxide, water and oxygen only one form of calcium sulfate being formed
    • C01B25/226—Hemihydrate process
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/32—Phosphates of magnesium, calcium, strontium, or barium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/32—Phosphates of magnesium, calcium, strontium, or barium
    • C01B25/322—Preparation by neutralisation of orthophosphoric acid
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/32—Phosphates of magnesium, calcium, strontium, or barium
    • C01B25/324—Preparation from a reaction solution obtained by acidifying with an acid other than orthophosphoric acid
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/32—Phosphates of magnesium, calcium, strontium, or barium
    • C01B25/327—After-treatment

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  • Chemical Kinetics & Catalysis (AREA)
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  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
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Abstract

Method for etching a source of phosphate containing or not containing calcium using sulphuric acid for a predetermined period of time from 20 minutes to 180 minutes under conditions in which the molar ratio between sulphate from sulphuric acid and optionally from the source of phosphate and calcium present in the source of phosphate is from 0.6 to 0.8 and P in the etching bath2O5The content is less than 6%.

Description

Method for etching phosphate source with acid
Technical Field
The present invention relates to a process for acid-etching a calcium-containing phosphate source to produce a purified phosphate-based compound, and to a process for acid-etching a calcium-free phosphate source to produce a purified phosphate-based compound.
Background
By "calcium-free phosphate source" is meant a source having a content of calcium bound or unbound to phosphate ions, hydrogen phosphate ions and/or dihydrogen phosphate ions of less than 10 wt.%, preferably less than 5 wt.%, preferably 1 wt.%, more preferably 0.1 wt.%, even more preferably 0.05 wt.% or less, relative to the total weight of dry matter of the phosphate source (dry at 105 ℃).
Sources of phosphate that do not contain bound calcium include, for example, iron phosphate, aluminum phosphate, lithium phosphate, zinc phosphate, magnesium phosphate, or mixed phosphates. In this embodiment, calcium is added to the phosphate source to provide SO in the etch bath4The molar ratio/Ca ranges from 0.6 to 0.8.
Acid etching of calcium-containing phosphate sources is well known in the art.
A conventional process with a similar effect involves reacting phosphate rock with sulfuric acid to cause calcium sulfate dihydrate or gypsum (CaSO)4.2H2O) crystallization. The gypsum slurry obtained in the first reactor may then be subjected to a slaking process in the second reactor which increases the size of the formed sulphate particles to improve filterability. The matured slurry is then filtered to obtain free P2O5About 25 to 35 wt% phosphoric acid.
It is also known that phosphoric acid produced by sulfuric acid etching produces higher temperatures and P2O5And/or SO3Calcium sulfate in the form of hemihydrate (CaSO) at a concentration4.1/2H2O) a slurry or a calcium sulfate slurry in the form of an anhydrate. These processes typically produce concentrated phosphoric acid and sulfate salts that are easily filtered, but this is doneIn some methods P2O5The extraction efficiency is not as high as that of the conventional method. After acid etching, the calcium sulfate hemihydrate obtained is converted, in some cases, to calcium sulfate dihydrate (Ullman's encyclopaedia of Industrial Chemistry,2008, pages 8and 9).
We also know a process in which phosphate rock is again subjected to etching conditions according to conventional methods to obtain a first slurry in which the gypsum formed has a particle size that provides good filterability. A portion of the first slurry is then sampled and subjected to conditions to convert gypsum to hemihydrate, thereby forming a second slurry. The remaining first slurry is mixed with the second slurry and the resulting slurry is then filtered (see WO 2005/118470).
The main problem affecting phosphoric acid production is the enrichment of P2O5Depletion of the deposit. These deposits have already been mined. Now we must rely on P2O5Minerals in which the content is considered to be low, e.g. P2O5Minerals in an amount of 25 wt% or less relative to phosphate rock, or in some cases P2O5Minerals in an amount of 20 wt% or less.
A process capable of using these minerals and extracting high quality production phosphoric acid therein is described in international patent application WO 2011/067321. The etching conditions of the method include significant stoichiometric reaction between the introduced sulfuric acid and the calcium contained in the phosphate rock, while the free P in the crystallized slurry is2O5The content is kept high between 38 and 50 wt% and the temperature is kept between 70 and 90 ℃. Surprisingly, these conditions produce very fine and stable dihydrate crystals. The slurry is then subjected to an elevated temperature during which the dihydrate particles dissolve and release P which is unetched or co-crystallized2O5Simultaneously realizes the crystallization of calcium sulfate hemihydrate with good filterability and free SO3Production of phosphoric acid with extremely low content. It should be noted that P2O5Minerals with low contents often have higher and higher contents of impurities.The impurity content is generally expressed in the following ratio: (Al)2O3+Fe2O3+MgO)/P2O5X 100, also known as MER (trace element ratio). Phosphates are considered typical, with MER ratios ranging from about 5 to 8.
Above 10, the impurity level is very important because at this point the impurities begin to adversely affect the crystallization of calcium sulfate in the gypsum form during sulfuric acid attack on the mineral. At this level of impurity content, the production of phosphoric acid becomes a problem, in particular because of the reasons affecting the crystallization of calcium sulphate dihydrate and its filtration. This is therefore a significant disadvantage in all processes where filtration is carried out immediately after the erosion of the phosphate rock.
In processes such as that described in patent application WO2011/067321, the crystallization of gypsum is also affected by impurities, but this is of no consequence since the gypsum is not intended to be filtered.
Document WO2012/163425 aims at developing a method for producing phosphoric acid by etching phosphate rock of poor quality, wherein sulfuric acid is used to enable high quality production phosphoric acid and good P to be obtained from the rock2O5And (4) extraction efficiency. Furthermore, the method must be capable of being applied in existing and traditional facilities and does not require expensive modifications that are not economically justifiable. According to this document, the method comprises: during etching, a source of fluorine is added to the first slurry, relative to the P contained in the phosphate rock2O5The fluorine source has a fluorine content in the range of 1 wt% to 5 wt%. The etching conditions are such as to provide a substantially stoichiometric reaction between the introduced sulfuric acid and the calcium contained in the phosphate rock, which is predominantly in the form of carbonates and calcium phosphates. The acidic aqueous phase of the first slurry resulting from etching contains no or little free sulfuric acid and free P2O5The content of (a) is relatively high.
It can be seen that the difficulty of producing phosphoric acid from phosphate rocks is always sufficient in etching yield, qualified acid and more or less variable calcium sulphate, in which caseIt is generally accepted that the etching of phosphate rock by concentrated sulfuric acid must be carried out in a stoichiometric reaction to produce crude phosphoric acid and ensure P2O5The extraction yield of (a) is sufficient and economically advantageous.
In the case of the production of phosphoric acid by etching phosphate rock with sulfuric acid by a stoichiometric reaction, the reaction is noted as:
(I)Ca3(PO4)2+3H2SO4→3CaSO4.2H2O+2H3PO4
wherein, SO4The molar ratio/Ca is 3/3, i.e. 1.
It is also known that the phosphoric acid thus produced can be used in combination with lime alkali to produce calcium hydrogen phosphate (DCP) for food grade (for humans or animals), or for any other application.
Document GB-938468 describes the production of monocalcium phosphate (MCP) or dicalcium phosphate (DCP) from phosphate rocks or natural minerals using hydrochloric acid.
Document WO 2015/082468 describes the etching of phosphate rock with hydrochloric acid.
Unfortunately, the hydrochloric acid etching process requires a DCP removal step to eliminate chloride ions that should not be present in, for example, certain grades of industrial DCP. The method using hydrochloric acid generates residual calcium chloride in which a part of impurities in the raw material is accumulated. This protocol requires additional purification to be carried out. Furthermore, the presence of hydrochloric acid in the etching bath at temperatures greater than or equal to 60 ℃ can lead to corrosion problems in the installation.
From document US3161466 we also know a method for etching phosphate rock using sulfuric acid. In the method described in this document, a first sulfuric acid etching is carried out in an etching tank to obtain a paste-like slurry, which can be aged or transferred to a second tank, in which it is subjected to a further acid etching. The method is based on a continuous pH control, increasing pH increase, for selectively precipitating different impurities present in the liquid phase (liquid). The liquid contained a large amount of MCP and phosphoric acid.
Unfortunately, this process requires strict pH control at each step due to the above selective precipitation and is economically unreasonable due to the multiple steps involved and the time required to treat phosphate rock, thus having limitations.
Finally, document GB793801 describes another process. In this document, the method described comprises the substoichiometric etching of phosphate rock with sulfuric acid at a concentration of 14% to 62%. The object of the described method is to recover the rare earths contained in phosphate rock. Thus, one of the key steps is to completely dissolve the phosphate rock to form a liquid phase from which rare earths can be extracted. Thus, the method includes the addition of reactive silica to keep the rare earths in solution and requires an etching time of about 24 hours. P disclosed in this document2O5Relative to the calcium content (P)2O5Ca) is from 10/1 to 4/1.
It can be seen that this method is time consuming and requires a significant expense to treat phosphate rock, but there is the fact that it can benefit by extracting rare earths of significant market value. However, in a process aimed at producing a purified phosphate-based substance, the economic efficiency of the process is necessarily questioned.
Disclosure of Invention
The object of the present invention is to remedy the drawbacks of the prior art by providing an economically profitable process with an optimum balance between: energy consumption, production costs, resistance of the materials used in the production plant and flexibility of the raw materials.
In fact, it is an object of the present invention to provide a method that enables the treatment of rocks with high phosphate concentrations as well as rocks with low phosphate concentrations and secondary phosphate sources.
To solve this problem, the present invention relates to a process for acid etching a calcium-containing phosphate source to produce a purified phosphate-based compound, as described in the opening paragraph, the process comprising the steps of:
a) presetting the phosphate source with sulfuric acid for 20 to 180 minutesAcid etching of the stages, forming a first suspension comprising a first solid matter and a first liquid phase, wherein the first solid matter is in suspension, the first solid matter comprises at least calcium phosphate and impurities, the first liquid phase comprises phosphoric acid and dissolved monocalcium phosphate, the etching is at a molar ratio of sulfate to calcium from sulfuric acid and possibly from a phosphate source of between 0.6 and 0.8 and P2O5The content is less than 6 percent;
b) subjecting the first slurry to a first filtration to separate the first solid matter from the first liquid phase; and
c) recovering a purified phosphate-based compound from the first liquid phase.
Advantageously, said P2O5The content of P dissolved in the first liquid phase2O5And (4) content.
SO4The molar ratio/Ca defines the amount of acid required to etch the Ca-containing phosphate source at the time the reagents are dosed.
Advantageously, the acid etching takes place in 1, 2 or more etching baths. It can be seen that the process according to the invention is an etching process under highly substoichiometric conditions, because of the molar ratio (SO) between the sulfate groups coming from the sulfuric acid and possibly from the phosphate source and the calcium present in the phosphate source4/Ca) between 0.6 and 0.8 has several advantages. First, consumption of sulfuric acid can be reduced by the process according to the invention and a variety of phosphate sources can be treated to produce a variety of purified phosphate-based compounds. In fact, the process according to the invention can be used to obtain a liquid phase containing phosphoric acid and monocalcium phosphate, from which also dicalcium phosphate can be obtained, thus offering great flexibility. Indeed, etching of dibasic calcium phosphate can be carried out to produce relatively pure phosphoric acid and its derivatives. Furthermore, the etching period is relatively short, thereby reducing production costs through the combined effect of the flexibility associated with the phosphate source and the diversity of the products obtained. Maintenance costs are also reduced due to reduced aggressiveness to the reaction environment.
To achieve a molar ratio between sulphate and calcium from the sulphuric acid and possibly from the phosphate source, the calcium content is mainly based on the calcium content in the phosphate source, but some calcium can often be added as required.
Advantageously, the method according to the invention comprises the following steps:
acid etching the phosphate source with sulfuric acid in 1, 2 or more etching tanks for a predetermined period of time from 20 minutes to 180 minutes, forming a first suspension containing a first solid substance comprising at least calcium phosphate and impurities and a first liquid phase comprising phosphoric acid and dissolved monocalcium phosphate, wherein the etching has a molar ratio between sulfuric acid and possibly sulfate from the phosphate source and calcium present in the phosphate source of from 0.6 to 0.8 and P in the etching tanks2O5The content is less than 6 percent;
subjecting the first slurry to a first filtration to separate the first solid matter from the first liquid phase; and
recovering a purified phosphate-based compound from the first liquid phase.
SO4The molar ratio of/Ca defines the amount of acid required to etch the Ca-containing phosphate source when the reagent is added to the one or more etching baths.
Advantageously, the method according to the invention comprises the following steps:
acid etching the phosphate source with sulfuric acid in 1, 2 or more etching tanks for a predetermined period of time from 20 minutes to 180 minutes, forming a first suspension containing a first solid matter comprising at least calcium phosphate and impurities and a first liquid phase comprising phosphoric acid and dissolved monocalcium phosphate, wherein the etching has a molar ratio between sulfate and calcium from sulfuric acid and possibly from the phosphate source of from 0.6 to 0.8 and P in one or more etching tanks2O5The content is less than 6 percent;
subjecting the first slurry to a first filtration to separate the first solid matter from the first liquid phase; and
recovering a purified phosphate-based compound from the first liquid phase.
SO4The molar ratio/Ca defines the amount of acid required to etch the Ca-containing phosphate source when the reagents are dosed in one or more etching tanks.
Advantageously, the step a) of acid etching comprises:
carrying out acid etching in an etching groove; or
Carrying out an acid etching in a first etching bath to which sulphuric acid is added, and subsequently transferring the first suspension formed or formed in the first etching bath to a second etching bath to which no sulphuric acid is added; or
Acid etching was carried out in two successive etching tanks with addition of sulfuric acid to the two tanks; or
Carrying out acid etching in three etching grooves; or
Carrying out an acid etching in a first etching bath to which sulphuric acid is added, and subsequently transferring the first suspension formed or formed in the first etching bath to a second etching bath and a third etching bath to which sulphuric acid is not added; or
The first and second etching baths are acid-etched with or without the addition of sulfuric acid, and the first suspension formed or formed in the first and second etching baths is transferred to a third etching bath without the addition of sulfuric acid.
In one embodiment of the invention, the method according to the invention comprises the following steps:
acid etching the phosphate source with sulfuric acid in an etching tank for a predetermined period of time of 20 to 180 minutes, forming a first suspension comprising a first solid matter in suspension comprising at least calcium phosphate and impurities and a first liquid phase comprising phosphoric acid and dissolved monocalcium phosphate, the etching being present in the sulfuric acid and possibly sulfate and phosphate sources from the phosphate sourceIs 0.6 to 0.8 and etches P in the tank2O5The content is less than 6 percent under the input condition;
subjecting the first slurry to a first filtration to separate the first solid matter from the first liquid phase; and
recovering a purified phosphate-based compound from the first liquid phase.
SO4The molar ratio/Ca defines the amount of acid required to etch the Ca-containing phosphate source when the reagents are introduced into the etch bath.
In one embodiment, the phosphate source does not contain any calcium. By "phosphate source free of calcium" is meant a calcium content of 10 wt% or less, preferably 5 wt% or less, preferably 1 wt% or less, more preferably 0.1 wt% or less, even more preferably less than 0.05 wt%, relative to the total weight of dry matter of the phosphate source (dry at 105 ℃).
The calcium-free phosphate source may be of mineral or organic origin, such as anaerobically digested ash of organic waste, e.g. manure, sludge from wastewater treatment plants, compost, manure, residues from the metal or chemical industry (including phosphate chemistry, food chemistry), sludge from wastewater plants, artificial fertilizers, manure and organic waste. They may also be present as phosphates of iron, aluminium, lead, zinc and magnesium. In this embodiment, calcium is added to the phosphate source to etch SO in the bath4The molar ratio of Ca/Ca amounts to 0.6 to 0.8.
Surprisingly, it appears that a combination of highly sub-stoichiometric conditions (using small amounts of sulfuric acid to etch the phosphate source) and shortened etching periods can be employed to produce purified compounds containing phosphate that are easily recovered and economically viable, albeit P in one or more etching tanks2O5Is reduced but still has sufficient purity to be useful for subsequent production including, but not limited to, production of food grade DCP on an industrial scale. Thus, in the process according to the invention, P is extracted from a variety of phosphate sources, regardless of whether the phosphate source has a high phosphate concentration or not2O5Is the bestIn (1). This means that once the process is carried out at the production site, the industrialist can mine both conventional ores with high calcium phosphate concentrations, and ores with lower calcium phosphate concentrations or any secondary products containing calcium phosphate.
By using a molar ratio between sulfate from sulfuric acid and possibly from the phosphate source and calcium present in the phosphate source of 0.6 to 0.8, the solid matter to liquid phase ratio is lower, i.e. the suspension density is lower. The sulphate present in the etching tank or tanks originates mainly from ore, but may also originate from a phosphate source and possibly from dilution water. In practice, the content of solid matter in the etching tank or tanks is generally less than 16%, preferably in the range 4% to 15%, so as to provide a suspension rather than a slurry, and the solid matter is present in low content, which is generally counter-intuitive in the treatment of phosphate sources where the etching time is short, the sulfuric acid is diluted and a filtration step is necessary.
In the process according to the invention, the reaction is sub-stoichiometric and has the following reaction formula:
Ca3(PO4)2+2H2SO4+H2O→2CaSO4.2H2O+Ca(H2PO4)2
wherein the theoretical SO4The molar ratio/Ca was about 0.66.
By using a molar ratio of sulphate from sulphuric acid and possibly from phosphate source to calcium present in the phosphate source in the range 0.6 to 0.8, in relation to the theoretical SO4The ratio/Ca is as close as possible, the etching conditions being such as to remain mainly under the precipitation curve of calcium and phosphate ions and thus to produce MCP soluble in the acidic liquid phase, where P is measured2O5The extraction rate of (2) is more than 90%.
In a specific embodiment, if the phosphate source does not contain calcium, the molar ratio of sulfate to calcium from the sulfuric acid and possibly from the phosphate source can be made 0.6 to 0.8 by adding calcium to the system.
The term "acid etching of a phosphate source with mineral acid, preferably sulphuric acid, for a predetermined period of time" is to be understood as meaning that the predetermined period of time is the average time spent in one or more etching tanks during batch etching or continuous etching, with possible recycling phases, as described below.
In the method according to the invention, the first solid matter comprises unetched calcium phosphates and sulfates (calcium sulfate hemihydrate, anhydrite or gypsum) and impurities. Calcium sulfate exists mainly in the form of gypsum (calcium sulfate dihydrate).
The term "monocalcium phosphate" is used to denote a compound having the general formula Ca (H)2PO4)2(MCP) compounds, known by various names, such as monocalcium phosphate, dicalcium phosphate, acidic calcium phosphate, monobasic calcium phosphate, monocalcium phosphate.
Advantageously, the predetermined period of time is less than 120 minutes, preferably less than 90 minutes, even more preferably less than 60 minutes, and in particular less than 45 minutes, even more in the order of 30 minutes.
It can be seen that the predetermined period of time during which the acid etching takes place can be shortened to achieve etching times as short as 60 minutes, especially 45 minutes, or even 30 minutes.
In a particular embodiment, P in one or more etching baths2O5The content is less than 5%, preferably P2O5Is in the range of 0.5% to 4%, and preferably in the range of 1.5% to 3%.
In fact, in the method according to the invention, P is etched in the medium2O5Is relatively low, but ultimately, unexpectedly, the P2O5Sufficiently pure to be recovered as a purified phosphate-based compound.
In a further preferred embodiment of the method according to the invention, the etching is carried out at ambient temperature.
In a preferred embodiment of the process according to the invention, the etching is carried out in one or more etching baths at a temperature of 90 ℃ or less, preferably 80 ℃ or less, preferably 75 ℃ or less, more preferably 60 ℃ or less, preferably above 40 ℃.
Indeed, in the present invention, it has been observed that ores can be treated by acid etching at generally lower temperatures (certainly at temperatures of 40 ℃ to 60 ℃), thereby eliminating the need for heat input and further reducing production costs from an energy consumption standpoint, while using dilute sulfuric acid, thereby reducing SO in the purified phosphate-based compounds3The residue of (1).
Advantageously, the sulfuric acid is dilute, particularly before being added to the etching bath, which reduces the cost of treatment for both phosphate sources, high and low phosphate concentrations, while also reducing the SO in the liquid phase3The content of (a).
Advantageously, in the process according to the invention, the dilute sulfuric acid has less than 14 wt%, preferably 13 wt% or less, preferably 10 wt% or less, more particularly in the range of from 0.5 to 9 wt%, preferably in the range of from 3 to 7 wt%, even more preferably about 5 wt% of H relative to the total weight of the dilute sulfuric acid2SO4And (4) concentration.
In another embodiment, the sulfuric acid is concentrated sulfuric acid and, in particular, is diluted in one or more etching tanks, wherein the dilution water may be drinking water, river water, sea water, recycled water, or water obtained from DCP production.
As previously mentioned, the molar ratio of sulfate from the sulfuric acid and possibly from the phosphate source to calcium present in the phosphate source ranges from 0.6 to 0.8, which is low enough to approach the optimum theoretical value and enables the MCP and phosphoric acid to remain in the liquid phase. The challenge is how to achieve calcium sulfate solubility without precipitation of calcium phosphate. Thus, advantageously, when the sulfuric acid is dilute sulfuric acid and has less than 14 wt%, preferably 10 wt% or less, even ranging from 0.5 wt% to 9 wt% of H relative to the total weight of the dilute sulfuric acid2SO4In conjunction with a shortened duration of the predetermined acid etch, by reducing the risk of precipitation of calcium and phosphate ions in solution and thereby favouring the formation of MCP and phosphoric acid in liquid phase rather than precipitated form in the etch bath or baths (because of the one or more of MCP and phosphoric acid)The reaction medium in the respective etching bath has been sufficiently diluted to prevent precipitation of calcium phosphate salts). Only calcium sulfate, preferably gypsum, is precipitated in amounts lower than in conventional methods of etching phosphate sources. Thus, in the process according to the invention, a recovered or recovered weak acid can be used.
In the process according to the invention, the sulfuric acid may be dilute sulfuric acid recovered from existing processes in the phosphate industry, metal industry, chemical industry, etc. For example, the liquid phase recovered after production of DCP by precipitation may be recycled to dilute the sulfuric acid etching solution. Preferably, the etching sulfuric acid is stored in a storage tank. Thus, the etching sulfuric acid may be recycled from other steps, or result from dilution with concentrated acid (sulfuric acid having a concentration of 98% or less), which may be diluted with water or a liquid phase (second liquid phase) recovered after generation of DCP, for example, by precipitation. Preferably, the sulfuric acid is diluted in the pipe during filling of the etching bath.
More specifically, in the process according to the invention, the molar ratio of sulfate coming from the sulfuric acid and possibly from the phosphate source to the calcium present in the phosphate source ranges from 0.68 to 0.78, preferably from 0.7 to 0.75.
More specifically, in the process according to the invention, the molar ratio of sulphate to calcium coming from the sulphuric acid and possibly from the phosphate source ranges from 0.68 to 0.78, preferably from 0.7 to 0.75, at the time of input.
Preferably, the method according to the invention comprises adding a base to the first suspension prior to filtration.
The addition of a base to the first suspension enables precipitation (pre-neutralization) of calcium fluoride prior to filtration, which may be advantageous depending on the desired final compound and its intended use. If the alkali added is a calcium alkaline compound, such as quick or slaked lime in powder form or milk of lime, or even limestone, gypsum formation prior to filtration is favored, which reduces residual SO in the liquid phase3And (4) content.
In another embodiment, the method according to the invention comprises: adding a base to the first liquid phase after filtration to form a second suspension comprising a second solid material suspended in a second liquid phase prior to the step of recovering a purified phosphate-based compound from the first liquid phase; and filtering the second suspension to separate the second solid substance in suspension from the second liquid phase, thereby recovering the second purified phosphate-based compound from the second liquid phase originating from the first liquid phase having a low content of second solid substance, wherein the second solid substance is mainly calcium fluoride.
In this embodiment, if the base has been added prior to filtration, calcium fluoride has been removed during filtration and is present in the first solid material, regardless of whether the desired purified phosphate-based compound is DCP or MCP and phosphoric acid. Production of DCP relies on the addition of calcium base to MCP (neutralization) resulting in the precipitation of calcium fluoride if it is not removed beforehand.
If no base is added before filtering the first suspension, the solid matter essentially comprises calcium sulphate compounds (calcium sulphate hemihydrate, anhydrite or gypsum), impurities and unetched phosphate, while the fluorine is still in the first liquid phase.
Calcium fluoride can be selectively removed when a base is added in a controlled manner to a liquid phase having a substantially reduced content of solid material but still containing fluorine. In this case, it is subsequently possible to consider carrying out different steps.
If the purified phosphate-based compound thus recovered from the second liquid phase is MCP and/or phosphoric acid, the second liquid phase is recovered and treated for this purpose.
If the purified phosphate-based compound thus recovered from the second liquid phase is DCP, the second liquid phase is treated by subsequent addition of a calcium base, such as quicklime or slaked lime in powder form or milk of lime, or limestone. In this case, a third suspension is formed in which calcium base is added to the second liquid phase having a low fluoride content, and this third suspension is then filtered to recover a third solid phase containing DCP.
Of course, when the DCP may contain fluorine or the phosphate source used is free of fluorine, a second suspension is formed by adding a calcium base, such as quick lime, slaked lime, lime powder or lime milk, or even limestone, to the first liquid phase, which is then filtered to separate off, on the one hand, the second solid matter containing DCP and, on the other hand, a second liquid phase forming residual water, which can be recirculated to form a sulfuric acid solution for acid etching of the phosphate source or for diluting the etching tank. In this case, there is no need for controlled addition of base to selectively precipitate fluoride.
In a specific and preferred embodiment, prior to filtering out the first solid material, a base is added to precipitate the fluoride and remove the fluoride from the first liquid phase having calcium sulfate and unetched calcium phosphate. The first liquid phase is then subsequently treated by adding a calcium base, such as quick lime, slaked lime, lime in powder form or in the form of milk of lime, or even limestone, to form a second suspension containing precipitated DCP as second solid matter, which is then recovered from the second suspension by filtration, centrifugation, decantation or any other solid-liquid separation method.
Regardless of whether DCP is formed from the first liquid phase or the second liquid phase, as described above, a stoichiometric amount of calcium base is added to the first liquid phase or the second liquid phase, e.g., in a neutralization reactor, to precipitate DCP, wherein the pH is preferably controlled in the range of 5 to 6.
A preferred way to precipitate DCP is to add finely ground limestone to the first or second liquid phase to neutralize the liquid phase containing MCP and phosphoric acid. The neutralization is preferably carried out for at least 30 minutes to complete the neutralization reaction and to bring the CO to completion2And completely released. In a preferred embodiment, in order to obtain a pH value ranging from 5 to 6, milk of lime is added to ensure complete precipitation of DCP, so as to be able to extract all the P in the residual liquid2O5。
More specifically, in the method according to the invention, the solid matter separated from the first liquid phase is partly or completely recycled by introducing it into the first suspension.
In practice, it is advantageous to increase the content of solid matter in the first suspension in the etching tank or in the filtering device, in order to facilitate the filtering of this first suspension or to be able to treat the residual calcium phosphate present in the first solid matter.
The first suspension containing calcium sulphate and possibly calcium fluoride is preferably recovered by any liquid/solid separation method (such as filtration apparatus, rotary filter manufactured by the applicant), by centrifugation, decantation, hydrocyclone or belt filter, to separate the first solid matter from the first liquid phase. The first liquid phase is P2O5In a slight excess, for example in the range from 0.05% to 0.6%, preferably from 0.1% to 0.25%, of sulphate.
During filtration, the filtration unit can be washed with water to remove interstitial water from the filter cake and recover traces of P remaining in the calcium sulfate cake2O5. Washing and separating the calcium sulfate. However, before this operation is carried out, the calcium sulphate is recycled in the etching tank or tanks to improve the etching conditions of the phosphate source and, thus, to improve the precipitation of the calcium sulphate forming the first solid substance and to facilitate its filtration.
It is therefore conceivable that the recycling operation is carried out by recycling a portion of the cleaned calcium sulphate to the etching tank, so as to increase the suspension density of the calcium sulphate to substantially more than 10% by weight relative to the total weight of the suspension.
It is also conceivable that the recirculation is carried out by setting the thickening agent of the first suspension before the separation, so that a portion of the thickened suspension can be sampled and returned to the etching tank.
This recirculation increases the density of the solid matter in the suspension or in the etching tank or tanks and helps to eliminate the supersaturation of calcium sulfate from the medium and/or etching tanks; this prevents uncontrolled nucleation of the suspension and enables crystalline calcium sulphate particles to be obtained in the first suspension. The recycling also prevents reactions that impede the sulfuric acid's etching reaction on the minerals.
In another embodiment according to the invention, the second solid matter separated from the second liquid phase is recycled by introduction into the first suspension and the second suspension. Preferably, when the second solid substance is calcium fluoride, it is not recycled.
For this purpose, in certain cases, if the filtration is complicated by a low solid matter content, it is advantageous to increase the solid matter content by introducing a second solid matter into the first suspension or the second suspension, for example by adding seed crystals.
In practice, when DCP is produced, the DCP-containing suspension is filtered or centrifuged to separate DCP from the liquid phase. Since the liquid phase is in fact water, there is no need to wash the separated DCP cake, and the liquid phase can advantageously be recycled in a sulfuric acid tank, in a pipeline or directly in one or more etching tanks. In some cases, when the purification of the first liquid phase is suitably carried out, the amount of impurities is reduced, which facilitates the recycling of the liquid phase recovered after separation of the DCP.
Preferably, the phosphate source is defined as any organic or mineral substance containing phosphate, which comprises at least 45 wt.%, preferably 40 wt.% or less, preferably 30 wt.% or less, preferably 20 wt.% or less, preferably 10 wt.% or less, of P relative to the total weight of dry matter (105 ℃ dry)2O5. In the phosphate source, calcium may or may not be bound to phosphate ions, hydrogen phosphate ions and/or dihydrogen phosphate ions. The source may be selected from the group of: traditional phosphate rock; p2O5Phosphate rock of low content; ashes of various mineral or organic origin, such as anaerobically digested ashes of organic wastes (e.g. fertilizers), sludge of wastewater treatment plants, compost, feces, residues of metal or chemical industries (including phosphate chemistry, food chemistry), sludge of wastewater treatment plants, bird droppings, ashes, fertilizers, feces and organic wastes.
In another embodiment, the phosphate source does not contain any calcium. For example, in this embodiment, the calcium content of the phosphate source is 5 wt%, preferably 1 wt%, more preferably 0.1 wt% or less, relative to the total weight of dry matter (105 ℃ dry). These phosphate sources include iron phosphate, aluminum phosphate or organic phosphates. In this way, calcium may be added in the form of lime, milk of lime, calcium carbonate, calcium chloride and possibly calcium-containing phosphate rock. The molar ratio between sulphate from sulphuric acid and possibly from a phosphate source and added calcium ranges from 0.6 to 0.8.
In general, in the case of calcium deficiency, this may be added in the form of lime, milk of lime, calcium carbonate, calcium chloride and possibly calcium-containing phosphate rock.
In the present invention, the term "conventional phosphate rock" is used to describe a typical P2O5Rocks more than 25% and which may or may not be reinforced are analyzed, i.e. the rocks are subjected to several physicochemical treatments (grinding, sieving, washing, flotation) to increase the titer of the rocks (P)2O5)。
In the present invention, the term "P2O5Low phosphate rock "is used to describe a typical P content of less than 25%, preferably 20%2O5And (6) analyzing.
The term "ash, sludge from wastewater treatment plants, ashes, fertilizers or phosphate content with respect to the total weight of the raw material P2O5Any raw material "of 40% by weight or less is used to describe a secondary phosphate source that is generally difficult to recover, such as ash from sludge from wastewater treatment plants, plant material (wood, wheat bran), small fired ash, incineration waste, or a by-product of biomass for power generation.
More specifically, in the process according to the invention, the purified phosphate-based compound is monocalcium phosphate MCP, dicalcium phosphate DCP, more particularly food grade dicalcium phosphate DCP (for human or animal consumption), phosphoric acid and its derivatives, such as acids directly derived from the first liquid phase or phosphoric acid produced from the DCP.
The term "calcium hydrogen phosphate (DCP)" is used to denote a compound having the formula CaHPO4Of dibasic calcium phosphate or dibasic calcium phosphate, which may be in anhydrous formA form of formula (DCPA) or dihydrate (DCPD).
The term "food grade Dibasic Calcium Phosphate (DCP)" is to be understood as any DCP used for animal consumption (especially feed grade and pet food), human consumption, and in the dental and oral care industries.
In a preferred embodiment of the process according to the invention, the second liquid phase is recirculated by introduction into the etching tank or tanks.
Further embodiments of the method according to the invention are shown in the appended claims.
The invention also relates to dicalcium phosphate, DCP, in anhydrous or dihydrate form, having a chloride content of 0.025% by weight or less relative to the total weight of the dicalcium phosphate, and/or a fluoride content of 2% by weight or less relative to the total weight of the dicalcium phosphate, and/or a Na content of 0.15% by weight or less relative to the total weight of the dicalcium phosphate2And (4) the content of O.
More particularly, the invention relates to dicalcium phosphate, DCP, in anhydrous or dihydrate form, having a chloride content of 0.02% by weight or less relative to the total weight of said dicalcium phosphate and/or a fluoride content of 1% by weight or less relative to the total weight of said dicalcium phosphate, in particular as an additive to animal feed.
Alternatively, the invention relates to dicalcium phosphate, DCP, in anhydrous or dihydrate form, having a chloride content of 0.02% by weight or less, relative to the total weight of said dicalcium phosphate, more particularly as fertilizer ingredient, or as phosphate source etched to produce phosphoric acid.
Further embodiments of the calcium hydrogen phosphate according to the invention are shown in the appended claims.
The invention also relates to the use of dicalcium phosphate DCP according to the invention in animal feeds, in particular feed grade (cattle, poultry, aquaculture, swine industry) and animal feeds for pets, said dicalcium phosphate DCP being in anhydrous form or in dihydrate form and having a chloride content of 0.02 wt% or less relative to the total weight of the dicalcium phosphate and a fluoride content of 1 wt% or less relative to the total weight of the dicalcium phosphate.
The invention also relates to the use of dicalcium phosphate DCP according to the invention, in particular in anhydrous form or in dihydrate form, and having a chloride content of 0.02% by weight or less relative to the total weight of the dicalcium phosphate, as an ingredient for fertilisers or as a phosphate source for the production of phosphoric acid.
The invention also relates to dicalcium phosphate DCP in anhydrous or dihydrate form, obtained by the process according to the invention.
Advantageously, the dicalcium phosphate DCP obtained in anhydrous or dihydrate form according to the process of the present invention has a chloride content of 0.025% by weight or less relative to the total weight of the dicalcium phosphate, and/or a fluoride content of 2% by weight or less relative to the total weight of the dicalcium phosphate, and/or a Na content of 0.15% by weight or less relative to the total weight of the dicalcium phosphate2And (4) the content of O.
More specifically, dicalcium phosphate DCP in anhydrous or dihydrate form, obtained according to the process of the present invention, has a chloride content of 0.02% by weight or less, with respect to the total weight of said dicalcium phosphate.
Advantageously, the dicalcium phosphate DCP obtained according to the process of the present invention, in anhydrous or dihydrate form, has a fluoride content of 1% by weight or less with respect to the total weight of said dicalcium phosphate.
Detailed Description
Further features, details and advantages of the invention will become more apparent from the following description, given without limitation by way of example.
The method according to the invention has a series of advantages which enable a competitive method to be carried out. In practice, the process of the invention can use dilute sulfuric acid or recycled sulfuric acid having a concentration, relative to the total weight of the dilute sulfuric acid, of, for example, less than 14% by weight, preferably between 0.5% and 10% by weight, in particular between 1% and 7% by weight, more in particular between 2% and 5% by weight, more in particular between 3% and 4% by weight,thereby reducing the cost of the raw materials. Without limitation, the sulfuric acid can be used to etch various phosphate sources, e.g., having low P2O5Rocks containing or secondary sources of phosphorus.
By reacting under substoichiometric conditions according to the invention with an SO of, for example, between 0.68 and 0.84the/Ca ratio is carried out, and the H can be saved by 20 to 25 percent2SO4And the extraction efficiency is advantageously made greater than 85%, and preferably greater than 90%.
The etching time is relatively short, reduced to 90 minutes or less, for example between 30 minutes and 60 minutes.
The etching temperature is also relatively low, for example between 40 ℃ and 60 ℃, compared to conventional etching methods, which allow good energy savings to be achieved, for example between 75 ℃ and 95 ℃.
P in the liquid phase of the first suspension relative to the total weight of the first liquid phase2O5The content preferably ranges between 1 wt% and 5 wt%, in particular between 1.5 wt% and 3.5 wt%, and even between 2 wt% and 3 wt%.
The process according to the invention can be further used to purify the As, Al, U, Th and Na contained in the phosphate source with a purification rate of more than 50%, preferably more than 60%, relative to the initial weight of these elements.
More particularly, the invention relates to, but is not limited to, DCP, for example obtained by the process according to the invention and having a chloride content and a fluoride content in food suitable for human or animal consumption, i.e. a chloride content of less than 0.025 wt%, even up to a content of 1ppm, and a fluoride content of less than 2 wt%, even up to a content of 0.1 wt%, relative to the total weight of the DCP.
Preferably, DCP contains a low content of residual SO due to etching by highly dilute sulfuric acid3. In certain embodiments, Na, relative to the total weight of DCP2The O content is also less than 0.15 wt%.
In an advantageous DCP product, the MgO content is also less than 1% by weight, relative to the total weight of the DCP.
More particularly, advantageous DCP according to the invention has a Sr content of less than 100ppm, preferably less than 50ppm, more particularly less than 10ppm, more particularly less than 1ppm, relative to DCP.
The DCP according to the invention further has a Th content of generally less than 5ppm with respect to DCP.
Similarly, the Mn content in the DCP according to the invention is less than 10ppm with respect to DCP.
Generally, the content of Mo in the DCP according to the invention is less than 2ppm with respect to DCP.
Finally, the DCP according to the invention preferably has a U of less than 32ppm3O8And (4) content.
Another object of the present invention is to provide a dibasic calcium phosphate DCP composition comprising
a) A CaO content of 40 wt% or more relative to the total weight of the calcium hydrogen phosphate,
b) a chloride content of 0.020 wt% or less relative to the total weight of the calcium hydrogen phosphate,
c) a fluoride content of 2 wt% or less relative to the total weight of the calcium hydrogen phosphate,
d) 0.15 wt% or less of Na relative to the total weight of the calcium hydrogen phosphate2And (4) the content of O.
It can be seen that DCP according to the invention has the qualities required for use in human and animal food and technical applications.
Examples
Example 1 laboratory Scale etching of phosphate Source
During an etching period of 30 minutes, 100g of a phosphate source (phosphate rock) are contacted with sulfuric acid diluted to a concentration of 2% in which SO is present at an etching temperature of 60 DEG C4The molar ratio/Ca was 0.8, wherein the phosphate source contained 30.5g of P relative to the weight of the phosphate source2O549.5 wt% equivalent CaO, 3.95 wt% fluorine, 0.308 wt% equivalent Fe2O30.547 wt% equivalent of Al2O3And 0.303 wt% equivalent MgO. SO (SO)4Definition of the molar ratio of/CaThe amount of acid required to etch the Ca-containing phosphate source when the etch cell is placed in service.
Once the additives were added, the composition was stirred for half an hour and then filtered.
The suspension was then vacuum filtered in a buchner funnel. The different amounts thus obtained were recorded and analyzed for calcium phosphate and liquid phase products.
In the laboratory protocol, batch processing is employed without cleaning. However, the washing was extrapolated and the P in the impregnating liquid of the filter cake was calculated2O5The amount of (c).
The etching yield was calculated by the following calculation formula: (P in the filtrate)2O5Mass of (2) + P in the impregnating solution of the filter cake2O5Mass of (c)/(P in phosphate Source)2O5Total mass of). P in the impregnating solution2O5The content corresponds to the P that can be recovered by washing the filter cake in an industrial process2O5。
The amount of dilute sulfuric acid added was 3499g, with SO4The content was 70.2 g. Due to the calcium content, SO, of the phosphate source4the/Ca ratio was 0.8.
The volume of the recovered liquid phase was 3.09 liters, the weight was 3125g, and the pH was 2.1. P in the liquid phase relative to the total weight of the liquid phase2O5Content of 0.83 wt%, and SO3The content was 0.16 wt%. P in the impregnating solution2O5The mass of (3) was 1.2 g.
CaO/P in the first solution2O5The molar ratio was 0.58, while the residual CaO content in the liquid phase was 0.19% by weight, relative to the weight of the liquid phase.
To P2O5The etch yield of (3) was 89%. It can be seen that, despite the use of low concentrations of 2% sulfuric acid and the sub-stoichiometric etching conditions and the total etching period of only 30 minutes, P is etched2O5The etch rate of (a) is still significantly higher.
Example 2 laboratory Scale etching of phosphate Source
According to the protocol of example 1, an etching period of 30 minutesIn the course of this, 150g of a phosphate source (rock) are brought into contact with sulfuric acid diluted to a concentration of 5%, in which SO is present, at an etching temperature of 40 DEG4The molar ratio/Ca was 0.8, wherein the phosphate source (rock) contained 15.8g of P relative to the weight of the phosphate source2O527.6 wt% equivalent CaO, 2.2 wt% fluorine, 2.37 wt% equivalent Fe2O32.88 wt.% of equivalent Al2O3And 0.416 wt% equivalent MgO.
The amount of dilute sulfuric acid added was 1131g, with SO4The content was 61.0 g. Due to the calcium content, SO, of the phosphate source4the/Ca ratio was 0.8.
The volume of the recovered liquid phase was 0.955 liter, the weight was 976g, and the pH was 1.8. P in the liquid phase relative to the total weight of the liquid phase2O5Content 1.97 wt%, and SO3The content was 0.27 wt%. P in the impregnating solution2O5The mass of (3) was 3.24 g.
CaO/P in the first solution2O5The molar ratio was 0.43 and the residual CaO content in the liquid phase was 0.33% by weight relative to the weight of the liquid phase.
To P2O5The etch yield of (3) was 95%. It can be seen that while a low concentration of 5% sulfuric acid is used with a very low phosphate content phosphate source and sub-stoichiometric etching conditions are employed with a total etching period of only 30 minutes for P2O5The etch rate of (a) is still significantly higher.
Example 3 laboratory Scale etching of phosphate Source
According to the protocol of example 1, 100g of a phosphate source (phosphate rock) is brought into contact with sulfuric acid diluted to a concentration of 5%, in which SO is present, at an etching temperature of 60 ℃ during an etching period of 30 minutes4The molar ratio/Ca was 0.8, wherein the phosphate source contained 30.5g of P relative to the weight of the phosphate source2O549.5 wt% equivalent CaO, 3.95 wt% fluorine, 0.308 wt% equivalent Fe2O30.547 wt% equivalent of Al2O3And 0.303 wt% equivalent MgO.
The amount of dilute sulfuric acid added was 1398g, with SO4The content was 70.1 g. Due to the calcium content, SO, of the phosphate source4the/Ca ratio was 0.8.
The volume of the recovered liquid phase was 1.13 liters, the weight was 1161g, and the pH was 2.2. P in the liquid phase relative to the total weight of the liquid phase2O5Content 2 wt%, and SO3The content was 0.20 wt%. P in the impregnating solution2O5The mass of (2) was 2.6 g.
CaO/P in the first solution2O5The molar ratio was 0.38 and the residual CaO content in the liquid phase was 0.30 wt% relative to the weight of the liquid phase.
To P2O5The etch yield of (3) was 85%. It can be seen that, despite the use of a low concentration of 5% sulfuric acid and sub-stoichiometric etching conditions and a total etching period of only 30 minutes therein, P is etched2O5The etch rate of (a) is still significantly higher.
Comparative example 1 laboratory-Scale etching of phosphate Source
According to the protocol of example 1, 100g of a phosphate source (phosphate rock) was brought into contact with sulfuric acid diluted to a concentration of 5% at an etching temperature of 60 ℃ during an etching period of 30 minutes, but in this case SO4a/Ca molar ratio of 1, wherein the phosphate source contains 30.5g of P relative to the weight of the phosphate source2O549.5 wt% equivalent CaO, 3.95 wt% fluorine, 0.308 wt% equivalent Fe2O30.547 wt% equivalent of Al2O3And 0.303 wt% equivalent MgO.
The amount of dilute sulfuric acid added was 1747g, with SO4The content was 87.2 g. Due to the calcium content, SO, of the phosphate source4the/Ca ratio was 1.
The volume of the recovered liquid phase was 1.4 liters, the weight was 1429g, and the pH was 2.1. P in the liquid phase relative to the total weight of the liquid phase2O5Content 1.63 wt%, and SO3The content was 0.61 wt%. P in the impregnating solution2O5The mass of (3) was 3.5 g.
CaO/P in the first solution2O5The molar ratio was 0.26 and the residual CaO content in the liquid phase was 0.17 wt% relative to the weight of the liquid phase.
To P2O5The etch yield of (3) was 88%. It can be seen that the comparative examples run under stoichiometric conditions consumed higher sulfuric acid for similar levels of etch yield. The calcium source required for neutralization will also be significantly higher.
Example 4 pilot scale sub-stoichiometric etching of phosphate rock
The pilot plant included 3 thermostatically stirred tanks with oil heated double shells. These troughs are continuous overflow troughs; the first two tanks have a capacity of 20 litres and the third tank has a capacity of 30 litres and serves only as a buffer tank before filtration.
10 liters of water were poured into the first tank and heated to operating temperature. A source of phosphate and dilute sulfuric acid are mixed with the desired etching conditions (SO)4Ratio of/Ca, etching duration for etching phosphoric acid source and H2SO4Concentration, P in etching bath2O5Content) was added to the first reactor at a corresponding flow rate.
The resulting suspension overflows into the second reactor. The second reactor is configured for neutralization prior to filtration. Neutralization prior to filtration is not performed systematically.
The suspension eventually overflows into the third reactor supplying the filtering unit.
The suspended amount was filtered every 30 minutes. Two types of filtering are performed alternately:
filtration for recycling was carried out in the etch reactor: the filter cake is not cleaned but is recycled in the first (etching) reactor to increase the proportion of solids in the reaction medium. The liquid phase (filtrate) was poured into a vat and stored for neutralization to produce DCP. This filtration step is certainly not required on an industrial scale. Of course, this filtration step may be performed, but is not required. This step can be advantageously carried out for pilot scale projects, as it preferably increases the amount of solid material in the etch reactor.
Filtration for calcium sulfate production: in this case, the calcium sulphate cake is washed with a predetermined amount of water to recover the P contained in the impregnation liquor2O5. The liquid phase and the washing filtrate were poured into a filtrate recovery bucket. The calcium sulfate was removed for evacuation.
The apparatus was allowed to stabilize and samples of calcium sulfate and liquid phase (filtrate) were collected for analysis and different products were also analyzed.
The yield was calculated as follows: p in liquid phase2O5Mass (g/h)/P in phosphate source of2O5Mass (g/h) of (1).
Adding a phosphate source in the form of rock to an etching bath in the presence of sulfuric acid diluted to 10 wt% with respect to the weight of dilute acid, wherein SO4The molar ratio/Ca is 0.8, wherein the phosphate source in rock form contains 30.3 wt% of P relative to the weight of the phosphate source2O547.6 wt% equivalent CaO, 3.68 wt% fluorine, 0.144 wt% equivalent Fe2O30.18 wt% of equivalent Al2O3And 0.542 wt% equivalent MgO. The etching temperature was 60 ℃ and the etching duration was about 1 hour. The pH in the etching bath was 2.04. The flow rate of the rock was 2.67kg/h and the flow rate of the acid was 17.5L/h. Etching P in the suspension relative to the total weight of the suspension2O5The content was 4.5 wt%.
During the filtration, the flow rate of the recovered liquid phase was 16.13 kg/h.
The etch yield was 93%.
It can be seen that the laboratory tests were confirmed by pilot plant projects and that low P was observed in the presence of dilute sulfuric acid and in the etch bath2O5Content of (A)<6%) and short etching periods, the etch yield for phosphate rock is particularly high when performed at sub-stoichiometric conditions.
Example 5 pilot scale sub-stoichiometric etching of phosphate rock
The pilot plant run was the same as the pilot plant run of example 4 and the same procedure was used as in example 4.
The same phosphate source as in example 4 was added to the etch tank in the presence of sulfuric acid diluted to 5 wt% relative to the weight of dilute acid, where the SO was due to the calcium content of the phosphate source4The molar ratio/Ca was 0.7. The etching temperature was 60 ℃ and the etching duration was about 1 hour. The pH in the etching bath was 2.5. The flow rate of the rock was 3kg/h and the flow rate of the acid was 35.6L/h. Etching P in the suspension relative to the total weight of the suspension2O5The content was 2.32 wt%.
During the filtration, the flow rate of the recovered liquid phase was 35.44 kg/h.
The etch yield was 94%.
It can be seen that, relative to example 4, although sulfuric acid was present twice as much as it was after dilution, P was present2O5The yield is even higher.
Example 6 pilot scale sub-stoichiometric etching of phosphate rock
The same pilot plant project as in example 4 was carried out, using the same method as in example 4, except that in the second reactor, i.e. the neutralization reactor before filtration, by adding Ca (OH)2Lime milk was used to adjust the pH to 2.48.
Adding a phosphate source in the form of a rock to the etching tank in the presence of sulfuric acid diluted to 5 wt% with respect to the weight of dilute acid, wherein, due to the calcium content, SO, of the phosphate source4a/Ca ratio of 0.8, wherein the sulfate source contains 34.9 wt% P relative to the weight of the phosphate source2O549.8 wt% equivalent CaO, 3.78 wt% fluorine, 0.136 wt% equivalent Fe2O30.386 wt% of equivalent Al2O3And 0.156 wt% equivalent MgO. The etching temperature was 60 ℃ and the etching duration was about 1 hour. The pH in the etching bath was 2. The flow rate of the rock was 2.6kg/h and the flow rate of the acid was 35.7L/h. Etching P in the suspension relative to the total weight of the suspension2O5The content was 2.10 wt%.
During the filtration, the flow rate of the recovered liquid phase was 38.22 kg/h.
The etch yield was 92%.
Example 7 pilot scale sub-stoichiometric etching of phosphate rock
The same pilot plant was conducted as in example 4, and the same procedure as in example 4 was employed.
Adding a phosphate source in the form of a rock to the etching tank in the presence of sulfuric acid diluted to 5 wt% with respect to the weight of dilute acid, wherein, due to the calcium content, SO, of the phosphate source4a/Ca ratio of 0.8, wherein the phosphate source contains 24.90 wt% of P relative to the weight of the phosphate source2O540.5 weight percent equivalent CaO, 2.54 weight percent fluorine, 3.97 weight percent equivalent Fe2O31.13 wt% equivalent Al2O3And 1.88 wt% equivalent MgO. The etching temperature was 60 ℃ and the etching duration was about 1 hour. The pH in the etching bath was 1.95. The flow rate of the rock was 3.19kg/h and the flow rate of the acid was 34.5L/h. Etching P in the suspension relative to the total weight of the suspension2O5The content was 1.82 wt%.
During the filtration, the flow rate of the recovered liquid phase was 37.91 kg/h.
The etch yield was 90%.
Example 8 pilot scale production of DCP from phosphate rock
For the production of DCP, a pilot plant run for etching of rock was used in a separate manner in the first etching. Thus, the items of equipment are used in sequence.
The pilot plant run was the same as the pilot plant of example 4. In this example, the liquid phase recovered from the filtration of example 7 was treated to precipitate DCP by neutralization in the following manner:
quicklime (or limestone) was added to the nominal flow in the reactor, into which also the liquid phase recovered from example 7 was introduced, with periodic control of the pH.
When the pH was equal to 5.5/6, the filtrate feed pump was started. The pH is periodically controlled and the feed rate of limestone or quicklime is adjusted to maintain the pH between 5.5 and 6.
The filtration from the buffer tank was performed every 30 minutes. Every second time, the calcium sulfate-containing filter cake is recycled in the first etch reactor to increase the ratio of solid matter in the reaction medium.
The production cake containing precipitated DCP was recovered and the mother liquor was stored in a bucket. Samples of the product (DCP and mother liquor) were collected for analysis.
The neutralization temperature was 60 ℃, the pH in the first tank was 4.4, and the pH in the second tank reached 5.55. The flow rate of the quicklime is 1.05 kg/h.
By the formula (P in DCP)2O5content/P originally present in MCP solution and acid2O5) To calculate the precipitation rate of DCP, P of operation2O5The result was 92%.
Comparative example 2 pilot scale sub-stoichiometric etching of phosphate rock
The pilot plant run was the same as the pilot plant run of example 4 and the same procedure was used as in example 4.
The same phosphate source as in example 4 was added to the etching bath in the presence of 20 wt% sulfuric acid relative to the weight of the acid, wherein the SO content, SO, was due to the calcium content of the phosphate source4The molar ratio/Ca was 0.8. The etching temperature was 60 ℃ and the etching duration was about 1 hour. The pH in the etching bath was 1.73. The flow rate of the rock was 5kg/h and the flow rate of the acid was 15.6L/h. Etching P in the suspension relative to the total weight of the suspension2O5The content was 7.10 wt%.
During the filtration, the flow rate of the recovered liquid phase was 13.3 kg/h.
The etch yield was 65%.
It can be seen that sulfuric acid is present in higher concentration relative to example 4, and that P is present2O5The content is more than 6 percent, and the yield is reduced to 65 percent.
It will be understood that the invention is in no way limited to the embodiments described above and that many modifications may be made thereto without departing from the scope of the appended claims.

Claims (15)

1. A process for acid etching a calcium-containing phosphate source to produce a purified phosphate-based compound, the process comprising the steps of:
a) acid etching the phosphate source using sulfuric acid for a predetermined period of time of 20 to 180 minutes, forming a first suspension containing a first solid matter and a first liquid phase, wherein the first solid matter is in suspension, the first solid matter comprises at least calcium phosphate and impurities, the first liquid phase comprises phosphoric acid and dissolved monocalcium phosphate, the etching ranges from 0.6 to 0.8 in molar ratio between sulfate from the sulfuric acid and possibly from the phosphate source and calcium present in the phosphate source and P2O5The content is less than 6 percent;
b) subjecting the first slurry to a first filtration to separate the first solid matter from the first liquid phase; and
c) recovering a purified phosphate-based compound from the first liquid phase.
2. The method of claim 1 wherein the acid etching is performed in 1, 2 or more etch baths.
3. The method of claim 1 or claim 2, wherein the predetermined period of time is less than 120 minutes.
4. A method according to claim 2 or claim 3, wherein P in the liquid phase is in one or more etching baths2O5The content is less than 5 percent.
5. A method according to any one of claims 2 to 4, wherein the etching is carried out in the one or more etching baths at a temperature of 90 ℃ or less.
6. A method according to any one of claims 2 to 5, wherein the sulfuric acid is in particular dilute sulfuric acid before being added to the one or more etching baths.
7. The method of claim 6, wherein the dilute sulfuric acid has a H of 13 wt% or less2SO4And (4) concentration.
8. The process according to any one of the preceding claims, wherein the molar ratio between the sulphate from the sulphuric acid and possibly from the phosphate source and the calcium present in the phosphate source ranges from 0.68 to 0.78.
9. The method of any one of the preceding claims, further comprising adding a base to the first suspension prior to filtering.
10. The method of any of claims 1-9, further comprising: adding a base to the first liquid phase after filtration to form a second suspension comprising a second solid material suspended in a second liquid phase prior to the step of recovering the purified phosphate-based compound from the first liquid phase; and filtering the second suspension to separate the suspended second solid substance from the second liquid phase, thereby recovering a second purified phosphate-based compound from the second liquid phase from the first liquid phase having a low content of the second solid substance.
11. The method according to any of the preceding claims, wherein the first solid matter separated from the first liquid phase is recycled by introducing the first solid matter separated from the first liquid phase into the first suspension.
12. The method according to any one of the preceding claims, wherein the calcium-containing phosphate source is selected from the group consisting of: traditional phosphate rock, low P2O5Phosphate rock, ash, wastewater treatment plant of contentThe content of the sludge, bone ash, pig manure, chicken manure, the ash of the sludge of a wastewater treatment plant, the sludge of the wastewater treatment plant and phosphate is lower than P relative to the total weight of the raw materials2O530 wt% of any starting material.
13. The process according to any of the preceding claims, wherein the purified phosphate-based compound is monocalcium phosphate, MCP, calcium hydrogen phosphate, DCP, more particularly food grade calcium hydrogen phosphate, DC P, phosphoric acid, such as an acid directly derived from the first liquid phase or phosphoric acid produced from the DCP.
14. The method of any one of claims 10 to 13, wherein the second liquid phase is recycled by introducing the second liquid phase into the one or more etchers.
15. A dibasic calcium phosphate DCP composition, the dibasic calcium phosphate DCP composition comprising:
a) a CaO content of 40 wt% or more relative to the total weight of calcium hydrogen phosphate;
b) a chloride content of 0.020 wt% or less, relative to the total weight of calcium hydrogen phosphate;
c) a fluoride content of 2 wt% or less relative to the total weight of calcium hydrogen phosphate;
d) 0.15 wt% or less of Na relative to the total weight of calcium hydrogen phosphate2And (4) the content of O.
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